The instant invention relates to molybdenum base alloys and to wires made from such alloys which wires are particularly useful as lead-in wires for use in glass quartz envelopes of electric light or lamps.
The use of molybdenum wire as lead-in wires for conducting current through a pinch seal of a glass or quartz envelope of an electric lamp is well known and frequently employed.
Thus, in Hardies, U.S. Pat. No. 4,015,165, molybdenum end wires (or outer current conductors) are employed to conduct current through a pinch seal to an molybdenum foil incorporated in the pinch seal to a current conductor provided within a glass or quartz envelope of an electric lamp.
Patrician et al, U.S. Pat. No. 4,322,248, shows a wire formed of an an alloy of molybdenum containing about 2 to 6% by weight of tantalum (as a gettering agent) and from about 50 to 1,000 parts per million by weight of silicon and about 50 to about 1,000 parts per weight of potassium as dopants. This Patrician et al patent teaches that the wires disclosed therein are useful as lead-in wires for conducting electricity into pinch seals of glass or quartz envelopes generally employed in electric lamps and as in particularly in halogen incandescent lamps.
The use of undoped molybdenum lead-in wires for conducting current through a pinch seal in a tungsten halide electric incandescent lamp is also shown in Van Dar Linden et al U.S. Pat. No. 3,538,373.
Similarly use is for molybdenum wires and foil is disclosed in Huyskens U.S. Pat. No. 3,736,454. Additionally, the use of molybdenum lead-in wires and foil conducting current through pinch seals in high pressure discharge lamps shown in U.S. Pat. Nos. 3,953,755, to Kuus et al; 4,539,509, to Varshneya; 4,389,201 to Hunsler et al and 4,302,699 to Keefe et al.
A problem with these molybdenum wires generally employed for lead-in wires is that they have a relatively low recrystallization temperatures. Thus a molybdenum wire (for example 30 mil diameter mandrel grade molybdenum wire) at 1100.degree. C. produces a completely recrystallized equiaxis grain structure resulting in a substantial loss in room temperature tensile strength. This loss in room temperature tensile strength increases significantly with increasing flashing temperature.
It is known that doping molybdenum with potassium and silicon to produce MOD grade molybdenum increases the recrystallization temperature to about 1650.degree. C. along with the formation of course elongated grain. As a result the MOD grade wire made from MOD grade molybdenum exhibits a substantially improved room temperature tensile strength and shows improved strength both at high and low temperatures in pinch seal applications in electric lamps.
However the production of the K-Si doped molybdenum is relatively time consuming and expensive. Thus, the method generally employed involves, slurry doping of molybdenum with the oxide of silicon and potassium, subjecting the powder to a two stage reduction including sintering in hydrogen, and pulverizing. Then the ingots are pressed and sintered and are then swaged and wire drawn.